Two distantly-related species that split 60 million years ago have produced an offspring on the forest floor of the French Pyrenees. We’re talking about ferns, but still, reuniting after such a long evolutionary breakup is roughly akin to an elephant hybridizing with a manatee, or us with a lemur, according to findings published in the March issue of American Naturalist.
Reproducing after that long is impossible for most species of plants and animals: the genetic incompatibilities will have become too vast. It only takes a few million years to become reproductively unsuited to each other -- a key condition for the evolution of new species. Until now, the most extreme examples have been tree frogs making baby frogs 34 million years after splitting into separate lineages, and sunfish hybridizing after a 40-million-year split.
This new unlikely love child made its way into a nursery from the mountains of France. Once there, a team led by Carl Rothfels from the University of British Columbia (formerly of Duke) extracted DNA from its fronds to identify its parentage. Their analyses revealed that the pale hybrid fern, xCystocarpium roskamianum, comes from a cross between an oak fern and a fragile fern. "To most people they just look like two ferns, but to fern researchers these two groups look really different," Rothfels explains in a news release. While the two can both be found co-existing throughout the northern hemisphere, they stopped exchanging genes and diverged from each other around 60 million years ago.
The researchers think that the parent ferns remained compatible after calling it quits so long ago because ferns don’t rely on the birds and bees, literally. Fern sex, like many other living organisms, brings the sperm together with the eggs. But all they need are wind and water, whereas lots of other plants depend on an animal pollinator. These animals might, over time, become pickier about flower shape or size or some other trait. “It's tempting to think that there's something special about flowering plants that gives them a competitive advantage,” Rothfels adds, “but these results raise a different possibility.”
Since ferns don’t rely on animals in this way, reproductive incompatibility for them probably just evolves more slowly. That’s probably why there are way more flowering plant species than fern species -- even though the latter have been around so much longer, predating even dinosaurs.